bummer

A bummer is an unlucky or disappointing event. Something that's a real drag.

When something goes wrong or doesn't work out as planned, people often call it a bummer. For example, if you were really looking forward to a big concert but they had to cancel it at the last minute, that would be a total bummer. You might also hear someone say "that's a bummer" when something unexpected and annoying happens, like getting stuck in traffic on the way home from work. Some people use this word even when it's not just about being unlucky - if they're really sad or depressed for some reason, that can be a bummer too. But overall, a bummer is just something that takes the fun out of your day.